Today, the development within the papermaking industry is focused on reducing the grammage of paper or board products while maintaining their strength properties. This trend is of high importance of both economical and environmental reasons. In order to produce paper or board products with lower grammage it is of interest to use low density fibers. However, one drawback with those pulp fibers is their poor ability to form strong fiber-fiber bonds which in turn results in insufficient strength properties.
WO 00/14333 relates to a method in which latex is used as a binder in the bulk layer to improve strength properties. However, WO 00/14333 suffers from high amounts of chemicals needed as well as problems related to the application of the latex binder. As an example, if latex is added to the wet end, retention problems of the latex on the fibers may cause deposit problems as well as disturbance of the wet end chemistry balance. Application problems may also occur if latex were added to already formed paper or board layers using existing equipment. Latex may also result in repulpability problems. One object of the present invention is to provide a method of providing low density paper or board laminate products while substantially maintaining the strength and/or stiffness properties. A further object of the present invention is to provide laminated paper or board products which can be repulped without problems in conventional repulpers. A further object is to provide a method of producing a paper or board laminate with improved binding capability of the fibers in at least one inner layer. A further object of the invention is to provide a paper or board laminate which has improved creasability. A further object of the invention is to provide a paper or board laminate in which at least one property of the paper including compression strength, edge wick resistance for hydrogen peroxide, bending resistance index, Z-strength and tensile stiffness index is improved. Particularly, it is an object of the present invention to provide a laminated paper or board, especially a low density laminate or a laminate comprising at least one low density board layer, which has improved compression strength as well as bending stiffness index and/or edge wick resistance.